Motors generally include a rotor and a plurality of coils that define a motor field. Running through the motor field is a three-phase electrical current. Although some motors have the motor field defined within the rotor, some motors have the field disposed within the stator. Particularly, flywheel type motors have a rotating flywheel for storing electrical power, field coils disposed in a stator, and magnets disposed in the rotor. The electrical current flowing through the stator field windings exerts a force on the rotor magnets, which causes the rotor and its flywheels to rotate.
Flywheels store power by rotating at relatively fast speeds such as 60,000–90,000 rpm. They can act as a battery by storing electrical power, and then discharging the electrical power by slowing down and producing a current in the field windings. Rotating flywheels at relatively high speeds presents difficulties. These difficulties limit the flywheel's rotational speed, and therefore the amount of power that can be stored in the flywheel.
One difficult with rotating a flywheel or any rotor at a relatively high speed with a motor is rippling or a variation in the torque which will cause variations in the speed and cause the rotor or flywheel to vibrate excessively or wobble and become damaged. One cause of this is the configuration of field windings in motors. Typically, field windings are disposed in an end to end relationship. The rotor permanent magnets experience a change in torque when passing the coil ends. The rotor tends to slow down as it passes by one of the coil ends and then accelerates as it begins to pass by another adjacent coil end. This can cause cogging of the rotor, which is detrimental to the rotor and can result in structural failure. Torque ripple can also excite resonances in the flywheel or other parts of the assembly. Another problem with motors is eddy currents. When rotating fast enough, eddy currents can nullify the driving force or generate sufficient heat so as to cause structural failure.
This invention includes motors that rotate rotors at relatively high speeds. In some embodiments, the problems encountered in the prior art with cogging and eddy currents are reduced or eliminated.